The present invention relates to an optical three-dimensional profilometry method based on processing SPECKLE images in partially coherent light, and to an interferometer implementing such a method.
When laser sources first came into use in the 60's, a curious phenomenon, known as the SPECKLE effect, was observed, and which is produced when the surface of an object of a roughness comparable with the wavelength of visible light (450-700 nm) is illuminated by a beam of coherent light, in which case, the surface of the object presents a granular appearance of randomly distributed light and dark speckles. The SPECKLE effect is caused by multiple interference of the rays reflected by the object, which present randomly distributed phases due to the roughness comparable with the wavelength; and theoretical analysis of the effect is extremely complex, mainly due to the statistic characteristics of the roughness of the object and the coherence properties of the light employed.
As the statistic distribution of the light intensity of a SPECKLE image is not directly related to the microscopic structure of the rough surface generating the image, traditional interferometry techniques are of no avail for determining the profile of the object.